pdbfmt: fix compiler warning [-Wmissing-braces]

If `PDBHdr->read` succeed, the structure is initialized anyway.

crengine/src/pdbfmt.cpp

@@ -714,7 +714,7 @@ class PDBFile : public LVNamedStream {
         _format = UNKNOWN;
         stream->SetPos(0);
         lUInt32 fsize = stream->GetSize();
-        PDBHdr hdr = { 0 };
+        PDBHdr hdr;
         PDBRecordEntry entry;
         if ( !hdr.read(stream) )
             return false;